ROBERT W. WITTE and ROBERT L. MC DONALD STANDARD MISSILE: GUIDANCE SYSTEM DEVELOPMENT To achieve a missile capability that is commensurate with the long-range, high data-rate, target­ detection characteristics of the AN/ SPY-IA radar, an evolutionary upgrade of the existing STANDARD Missile-l was authorized. Designated STANDARD Missile-2, it adds a command mid­ course flight phase, thereby providing the AEGIS Combat System with increased intercept range and higher firepower . STANDARD Missile-2 with inertial midcourse guidance also provides upgraded TERRIER and TARTAR Combat Systems with a corresponding increase in capability. Terminal guidance accuracy has also been improved by incorporating a new homing receiver common to all STANDARD Missile-2 variants. INTRODUCTION The design evolved over a two-year period, during which frequent meetings were held to review every The development of STANDARD Missile-2 (SM-2) aspect of the signal processing and logic. During that began in the early 1970's, with General Dynamics/ time, the communication links had progressed to the Pomona as the Design Agent and APL as Technical point where hardware interface tests were being con­ Advisor. At the time, STANDARD Missile-l (SM-l) ducted to demonstrate ship system compatibility. was in production as the primary weapon for Fleet Prior to the beginning of flight testing at White air defense by TERRIER and TARTAR ships. The Sands Missile Range in 1975, a guidance section principal modification to SM-l envisioned at the out­ design model was supplied to APL for an assessment set was to add a midcourse guidance system consist­ of its performance. Hundreds of hours of tests were ing of communication links, a digital guidance com­ conducted in the Guidance System Evaluation Labo­ puter, and an inertial reference unit. These additions ratory. As that evaluation proceeded, SM-2 began to were incorporated as shown in Fig. 1. For terminal acquire a reputation as a highly accurate missile. The guidance, the original plan had been to use the exist­ results obtained in the APL tests were confirmed in ing SM-l scanning receiver. However, shortly after subsequent flight tests of SM-2 and an upgraded SM-l becoming the Naval Sea Systems Command AEGIS that also uses the new homing receiver. To date, both Project Manager in 1972, Rear Admiral W. E. Meyer missiles have achieved a sizable percentage of direct made the decision to include a new monopulse ter­ hits in intercepting target drones. minal homing receiver. Thus, the final SM-2 configu­ The development and deployment of SM-2 cannot ration consisted of a largely new guidance section, a realistically be a stopping point in providing the fu­ repackaged autopilot to accommodate the inertial ture Navy with an effective antiair warfare capabil­ reference unit, and the existing SM-l ordnance, pro­ ity. Because the threat has continued to increase, the pulsion, and steering control systems. initial SM-2, now designated Block I, is being im­ To accelerate the development of the new homing proved. Currently, Block II is in engineering develop­ receiver, General Dynamics/ Pomona and APL engi­ ment, with APL technical support being provided in neers embarked on an intensive cooperative effort. many areas, including guidance. SM -2 UPGRADE Figure 1 - STANDARD Missile-1 Communication linkS/Digital guidance computer (SM-1) showing STANDARD Missile- Monopulse receiver I / Inertial reference unit 2 (SM-2) additions. Evolutionary im­ provements to STANDARD Missile have been facilitated by the use of modular packaging. The SM-2 up­ grade consisted of a new guid­ -~ ance section and additions to the fmprncrf:---; autopilot/battery section, while R,dome I Gu;d,noe \ Au,op;lotlb'tte", Ro,ke'mo'o' S'eedng oon'<o1 other sections remained essen­ Seeker antenna Ordnance tially unchanged. Vo lullle 2, N Ulllber4, 1981 289 MISSILE GUIDANCE TECHNIQUES either target-reflected energy from shipboard illu­ mination or jamming energy emanating from the tar­ Semiactive Guidance get. The seeker consists of a gimballed antenna and a A feature common to both SM-l and SM~2 is an radar receiver that measures the angle of arrival of ability to "home," i.e., to guide either some or all of the received signal (Fig. 2). The seeker tracks the tar­ the flight by means of target-reflected energy. The get and provides information to the missile guidance source of this energy is a high power, continuous computer concerning the line-of-sight angle and the wave, shipboard radar illuminator. A portion of the closing velocity as determined from the Doppler fre­ illuminator signal is received directly by the missile quency. Using a proportional navigation steering for use as a Doppler frequency reference. To accom­ law, discussed below, the guidance computer gener­ plish this, the illuminator antenna combines a narrow ates steering commands that ideally keep the missile beam directed toward the target with a broad refer­ on a collision course with the target. ence beam that encompasses the missile throughout Semiactive, home-all-the-way guidance is used in flight (Fig. 2). This type of guidance is called "semi­ many missile systems throughout the world. Its pri­ active" because the transmitter and receiver, al­ mary advantage is that it provides moderately good though linked, are not colocated. area defense coverage, i.e., intercept range, by virtue A semiactive missile must also be able to home pas­ of high power ship-based or ground-based illumina­ sively on electronic countermeasures signals radiated tion combined with up-and-over flight trajectories. by the target. Such signals may be used to screen the (Such trajectories are achieved by launching the mis­ target-reflected signal or otherwise deceive the semi­ sile at a relatively steep angle and allowing it to climb active receiver. Home-on-jam processing is automati­ above the target early in flight so as to better main­ cally selected when the target skin return cannot be tain available kinematic energy.) One of the major identified and when incoherent energy is present limitations of home-all-the-way guidance is its rela­ whose frequency and angle of arrival are approxi­ tively low firepower, since one of only a few illumi­ mately correct. nators must be committed to a single target for the entire missile flight. A second limitation is illustrated Home-All-the-Way Guidance in Fig. 4, which shows the many signals that may be A home-all-the-way guidance ' policy is one in present at the missile's receiving antenna. Clearly, a which the missile derives its own steering commands missile receiver that must pick out the target signal throughout flight based on the processing of signals immediately after launch has a much more difficult received from the target. Such a policy requires that task than it would if acquisition could be delayed un­ the target be acquired either prior to or shortly after til later in flight. launch. Figure 3 illustrates the various phases in the firing of an SM-l, which uses home-all-the-way guid­ Midcourse Plus Terminal Guidance ance. On the launcher, the missile is provided with a Midcourse guidance implies an intermediate flight post-launch prediction of where it should look for phase in which an external source supplies sufficient the target in angle and Doppler frequency. Following information to allow the missile to guide or steer an unguided boost phase, the missile seeker acquires toward the target without having to home. Two types Missile Guidance System Figure 2 - Semiactive guidance concept. Both SM-1 and SM-2 em­ ploy continuous wave, semiactive guidance. The target is illumi­ Steering commands~-.:.-~ nated by highly pure, sinusoidal to autopilot RF energy that allows objects to be distinguished on the basis of their velocity by the Doppler shift of the reflected energy. Homing is semiactive in the sense that the transmitter, in this case a high power shipborne radar, and the missile receiver are linked but not colocated. A passive homing ca­ pability is also provided to cope with possible jamming by the tar­ get. The combination of the on­ board homing receiver and the steerable front antenna is known as a "seeker." In addition to target tracking, the seeker supplies in­ formation to the guidance compu­ ter for computing missile steering commands. 290 Johns Hopkins APL Technical Digest Endgame efficiently to engage a larger number of targets. If the • Target detection by fuze • Warhead detonation missile has the kinematic capability and if the mid­ course trajectory control is sufficiently accurate, then -C.,r\'/,:)) a small target can be engaged at a longer range than ~-Y~' would be possible if seeker acquisition were required Homing Phase early in flight, as in the home-all-the-way case. • Missile homes to target • Semiactive or home-on-jam The shorter missile-to-target propagation distance guidance at the start of the terminal homing phase also tends to enhance the target return relative to some of the sources of interference shown in Fig. 4. In particular, Midcourse Phase (SM-2 only) the missile has a much better chance of "seeing" the • Missile flies to vicinity of target target in the presence of standoff jamming following • Guidance intelligence supplied by ship a period of midcourse guidance than it would imme­ diately after launch. L Boost Phase 1;'~ ( • Missile achieves supersonic speed ~ • Unguided flight STANDARD MISSILE-2 Initial ization MIDCOURSE GUIDANCE • Missile on launcher • Initialization data supplied by ship Midcourse guidance has been implemented in SM-2 by adding to SM-I an inertial reference unit together Figure 3 - STANDARD Missile operational sequence. On the launcher, the SM-1 is supplied with target acquisition with missile-ship communication links. The inertial data and begins homing shortly after the unguided boost reference unit consists of an instrument package cou­ phase of flight.